Can I offer some advice here and you willingly listen to it? Don't, you'll spend more than double what it will cost by the time you are done. Trust me on this, I'm not being a dick and all, "This guys a fing noob and doesn't know anything!", but I speak from experience on these matters. I hate seeing people spend hard earned money on stuff they simply just don't need to. That's the last I will comment on the subject, but if you decided to do this I will help you as best I can.

I did it, don't let them talk you out of it. See, what you do is you put something called a "for sale" sign up on your WRX and then somebody will give you money. Then you find an STi with the same sticker int he window, poney up the difference, and BOOM! EJ257 with 6-speed. Magic.